Conventional cooling systems have at least one head coolant jacket, one block coolant jacket, a main coolant pump that frequently is a mechanical pump, an auxiliary coolant pump that frequently is an electric pump, a radiator, a thermostat, a heat exchanger, a vapor separator, and further components and corresponding connecting lines. Below a specific coolant temperature of, for example, 90° C., the coolant flows through the main coolant pump, the coolant jackets, the heat exchanger, the oil cooler, the vapor separator and the thermostat, i.e. through the “small cooling circuit”. Once the specific temperature has been reached, the thermostat opens and, as a result, the coolant additionally flows through the radiator in parallel with the heat exchanger.
The practice of allowing separate flows of a coolant in a coolant circuit through the engine block and the cylinder head of the internal combustion engine, respectively, is known. In this way, the cylinder head, which is coupled to the combustion air especially by the combustion chamber and port walls, and the engine block, which is coupled thermally especially to the friction points, can be cooled differently. A “split cooling concept” (separate coolant circuit) is intended to ensure that the cylinder head is cooled when the internal combustion engine is in the warm-up phase, the intention being that there should initially be no cooling of the engine block, thus allowing the engine block to be brought to the required operating temperature more quickly.
In order to improve the warm-up behavior of the internal combustion engine, a “no-flow strategy” can be employed, in which there is no flow of coolant through the block water jacket. For this purpose, an additional shutoff valve is provided, with the thermostat being replaced by a proportional valve and the mechanical pump furthermore being replaced by an electric pump. The mechanical pump is driven the internal combustion engine, and the electric pump is driven by a controllable electric motor.
As an alternative, it is therefore possible to improve the warm-up behavior by combining the split-cooling concept with the no-flow strategy, the result being that the cylinder block is not cooled while the cylinder head is cooled.
However, the prior systems also may include the practice of providing internal combustion engines with an auxiliary coolant pump in order to improve the endurance of the internal combustion engine, especially the turbocharger thereof, in “hot soak phases”, i.e. in phases after an engine has been switched off in a warm environment.
According to the current conventional construction, exhaust turbochargers have a rotor with a compressor impeller and a turbine wheel and a shaft which is arranged between the compressor impeller and the turbine wheel and is rotatably mounted on the turbine side and on the compressor side in corresponding rotor bearings. The rotor bearings may generally be plain bearings or rolling contact bearings with oil lubrication. The bearings are generally supplied with a lubricant, e.g. engine oil, which is passed to the individual bearing locations via a pressure line, for example. In addition to lubricating the bearings, the purpose of the lubricant is also to cool the latter. Cooling is very important, especially for the turbine-side bearings since a significant amount of heat is introduced into the shaft by the hot turbine wheel.
An operating state which is particularly difficult to manage for this reason is the rapid shutdown of the internal combustion engine from an operating state involving a high load. The supply of lubricant is interrupted when stopping, and the dissipation of heat from the shaft is no longer assured. The result is overheating of the lubricating oil and associated carbonization of the lubricating oil remaining in the exposed parts of the bearing assembly owing to the continued heating of the shaft caused by the hot turbine. Ultimately, the carbonization of the lubricating oil leads to fouling of the rotor bearings and this frequently causes damage to the turbocharger.
The abovementioned critical operating state, i.e. the rapid shutdown of the internal combustion engine from an operating state involving a high load, can be observed especially on motor vehicles with an “automatic start/stop system” since this system automatically switches off the internal combustion engine if there is no need for motive power to drive the motor vehicle (stop state), e.g. when stopping at a traffic light.
To avoid this, provision is made to incorporate the turbine casing into the coolant circuit and to cool it by means of the electric auxiliary coolant pump by bringing about a flow of coolant in the turbine casing.
However, the electric auxiliary coolant pump is also supposed to supply the cabin heat exchanger with coolant during the stop phases of the internal combustion engine. It is helpful in such cases to use what are as it were additional sources of heat, such as the turbine casing and/or exhaust manifolds integrated into the cylinder head.
During the warm-up phase, however, the coolant limit temperature (specific temperature), in the turbine casing, for example, and/or of the exhaust manifold may be reached sooner than in other areas, such as in the cylinder block and/or at the fresh air side of the cylinder head. Thus, the “no-flow strategy”, for example, is abandoned owing to the high coolant temperature even though the cylinder liners, for example, have still not heated up and are therefore virtually cold.
The inventors herein have recognized the issues with the above approaches and provide an engine system to at least partly address them. In one embodiment, an internal combustion engine comprises a cabin heat exchanger circuit including a connecting line opening on an inlet side into a cylinder block coolant jacket, a main coolant pump arranged in the cabin heat exchanger circuit, an auxiliary coolant pump arranged in the connecting line, and a check valve.
In this way heating passenger cabin and cooling of the engine and/or turbine may be supplemented with an auxiliary coolant pump while providing a simplified system, thus increasing engine efficiency and further improving the cooling and/or warm-up behavior of the internal combustion engine.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.